1. Field of the Invention
This invention relates generally to the construction and operation of device arrays and, more particularly, to arranging heat producing devices into an array and operating them in accordance with device thermal operating restrictions to avoid hotspots.
2. Description of the Related Art
It frequently is necessary to arrange multiple heat producing devices into an array for simultaneous or near simultaneous operation. Common examples include arranging electronic components on a circuit board and also operating magnetic disk drive storage devices in an array. The heat produced by the devices typically affects the operation and lifetime of the devices so that they must be spatially separated in the array according to thermal restrictions. The thermal restrictions typically are established to prevent local overheating or "hot spots" that otherwise would produce adverse heating effects.
In the case of arranging electronic heat-producing components, for example, the task might be represented by placing the components on the circuit board by dividing the board into a grid, or two-dimensional array, of cells into which the components are placed such that no overheating occurs. The case of arranging and operating a magnetic disk drive array can best be represented by the technique of storing data across redundant arrays of inexpensive disks, a storage array architecture commonly referred to by the acronym RAID. In the RAID technique, an array of relatively inexpensive disk storage devices is provided and data is stored in multiple locations distributed across the array of disk devices. In some variations of the RAID technique, corresponding parity data also is stored.
Each disk device of a RAID system typically includes multiple cylinders or platters that receive data for storage and includes a separate heat producing drive motor. A RAID system typically includes from ten to one hundred disks housed in spaced apart racks that permit cooling air to flow between devices. The dam, typically comprising multiple records, is duplicated or in some cases subdivided and stored across the drives in clusters at different respective locations of the disks according to a predetermined pattern. For example, the same data might be stored on the second platter of the first drive, the third platter of the second drive, the fourth platter of the third drive, and so forth until it is stored on the first platter of the last drive. Other data records would be similarly stored. A large variety of storage patterns can be followed for storing data. Likewise, data that is to be retrieved from the array in a read operation is extracted from the disks according to the same pattern and is reconstructed.
Such an arrangement of data across disks is commonly referred to as "striping" and advantageously permits data recovery if one of the disk units fails. Thus, clusters of disk drives within the array are accessed with each data storage operation so that each disk drive in a cluster that is accessed incurs a disk operation. The disk storage devices each generate heat when they are accessed and therefore the devices must be spatially separated. Configuring the devices into clusters ensures that the number of devices operated with each storage operation likely will not violate the device thermal restrictions. Other techniques are known for configuring clusters of multiple disk devices in arrays to distribute storage operations and avoid overheating.
Conventional RAID systems typically include arrays of from ten to one hundred disks. The recent trend in data storage systems is to larger and denser RAID systems that can exceed conventional packaging and power handling capabilities. For example, a disk array that is to provide 10-terabyte of storage that consumes power at a typical rate of 50 mW per megabyte would require 500 kW of input power to service the disk devices. This amount of input power would create a cooling problem that would be unacceptable to most users and could involve the placement of thousands of disk drives. Methods for configuring clusters of devices in a disk array can be relatively complicated and can require substantial computing resources. Similarly, determining a satisfactory arrangement of electronic components on a circuit board can become difficult with the increasing density of device packaging.
From the discussion above, it should be apparent that there is a need for a system that determines a configuration of heat producing devices in an array so that thermal restrictions are satisfied to prevent local overheating or "hot spots" from occurring without need for substantial computing resources. The present invention satisfies this need.